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## $Id: __init__.py 1601 2010-07-18 19:35:43Z css1hs $
## -*- coding: utf-8 -*-
# jpeg.base
# =========
#
# .. module:: pysteg.jpeg.base
#
# :Module: pysteg.jpeg.base
# :Date: $Date: 2010-07-18 20:35:43 +0100 (Sun, 18 Jul 2010) $
# :Revision: $Revision: 1601 $
# :Copyright: © 2010: University of Surrey, UK
# :Author: Hans Georg Schaathun <H.Schaathun@surrey.ac.uk> (2010)
#
# ::
from numpy import array, vstack, hstack, kron, ones
# The sysrnd variable is defined here for the benefit of other submodules::
from random import SystemRandom
sysrnd = SystemRandom()
# ::
def uMask(u=7):
return array([ [ (x+y<u) & (x+y>0) for x in range(8) ] for y in range(8) ])
# Make a mask to extract AC coefficient
acMaskBlock = array (
[ [ False ] + [ True for x in range(7) ] ] +
[ [ True for x in range(8) ] for y in range(7) ]
)
def acMask(h1,w1,mask=acMaskBlock):
"""Return a mask of the given size for the AC coefficients of a
JPEG coefficient matrix."""
(h,w) = (h1/8,w1/8)
A = vstack( [ mask for x in range(h) ] )
A = hstack( [ A for x in range(w) ] )
return A
def repmat(M,rep): return kron( ones( rep ), M )
def getfreq(A,i,j):
"""
Return a submatrix of a JPEG matrix A including only frequency (i,j)
from each block.
"""
(M,N) = A.shape
return A[xrange(i,M,8),:][:,xrange(j,N,8)]
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